Scoliosis refers to a complex deformity of the spine in three planes. It is diagnosed by measuring the angle of curvature of the spine (a Cobb angle of at least 10°) in the frontal plane and the axial rotation in the horizontal plane, as well as being characterized by spinal deformities in the sagittal plane ^[1][2][1,2]. Adolescent idiopathic scoliosis (AIS) is a three-dimensional spine deformity. It is a structural, lateral, rotated curvature of the spine that arises in otherwise healthy children at or around puberty ^[3][4][3,4]. Although scoliosis can be diagnosed at any age, the majority of cases are detected during adolescence between 10 and 18 years ^[2][3][4][5][2,3,4,5]. Scoliosis is the most common pediatric deformity of the spine ^[6][7][6,7]. The International Society on Scoliosis Orthopaedic and Rehabilitation Treatment (SOSORT) has estimated that the global incidence of adolescent idiopathic scoliosis (AIS) in pediatric population ranges from 0.93% to 12% [8].

Adolescent idiopathic scoliosis is a multifactorial disease with intrinsic and extrinsic alterations. The key points of the etiology and pathogenesis of AIS were found to be related with changes in almost every field from genetic to environmental factors [4]. However, about 80% of scoliosis cases present with idiopathic scoliosis of unknown etiology [8]. Scoliosis is called idiopathic when no other underlying disease can be identified [9].

Inappropriate treatment of AIS can result in severe deformities of the trunk, back, and chest, disturbing the functional biomechanics of the body, limiting lung volume, and reducing physical capacity, work capacity, and quality of life [8]. Although scoliosis has long been thought to be a harmless condition, evidence indicates that people with scoliosis are more prone to experience back pain ^[10][11][10,11]. Scoliosis causes disability of varying severity and poses a high healthcare burden, particularly when patients require extensive surgical treatment ^[12][13][12,13]. Due to the complexity of the procedure, the surgical treatment for scoliosis involves a relatively high cost and risk of complications. Because the risks associated with mild and moderate scoliosis are very high, conservative treatment is preferred to stabilize the deformity and improve the quality of life.

As idiopathic scoliosis is characterized by a complex pathomechanism, a comprehensive treatment plan is essential for its conservative management. One of the best approaches for scoliosis management is to use physiotherapeutic scoliosis-specific exercises (PSSE). The SOSORT uses the term physiotherapeutic scoliosis-specific exercises (PSSE) for all schools and methods approved by the organization. Every method and school incorporate the principles of the SOSORT guidelines and share a common mission. A PSSE physiotherapy methodology must be based on scientific evidence and customized for each patient ^[14][15][14,15]. The SOSORT consensus attributes to the “3D self-correction” first place in the ranking of important elements to be included in the exercises ^[16][17][16,17]. Self-correction can be defined as the search for the best possible alignment the patient can achieve in the three spatial planes [18].

The SOSORT emphasizes that PSSE physiotherapy used for the treatment of AIS differs from nonspecific physiotherapy in that it aims at three-dimensional self-correction of posture, stabilization of corrected posture, patient education, and the integration of corrective positions into daily activities [8]. The frequency of PSSE physiotherapy varies from 2 to 7 days per week, depending on the complexity of the technique used, the need of the patients, and their ability to follow the prescribed program. Long-term outpatient programs typically occur two–four times a week if the patient is ready to cooperate [15]. Typically, PSSE physiotherapy is only performed by professionally trained instructors, as physical exercises are chosen based on the type and severity of scoliosis in each patient, and the nature of the exercises themselves depends on the methodology applied [8].

The most well-known PSSE physiotherapy schools operating under the SOSORT are as follows [15]:

• Schroth, Germany;
• Lyon, France;
• SEAS (Scientific Exercise Approach to Scoliosis), Italy;
• BSPTS (Barcelona Scoliosis Physical Therapy School), Spain;
• Side Shift, UK;
• DoboMed, Poland;
• FITS (Functional Individual Therapy of Scoliosis), Poland; and
• FED, Spain.

Each PSSE physiotherapy methodology has been developed and applied in different European countries. Several other methodologies are also commonly used in different continents, but their principles are similar to those used in Europe.

Despite the fact that each of these schools has developed a separate methodology for the treatment of scoliosis and has been applying it for decades, the scientific validity of both PSSE physiotherapy and nonspecific physiotherapy in the treatment of AIS remains in question ^[19][26]. According to the Cochrane Systematic rResearchview, scientific works published prior to 2012 do not provide strong evidence supporting the effectiveness of physiotherapy in the treatment of AIS ^[20][21][27,28], but subsequent publications have confirmed that physiotherapy can help reduce the Cobb angle of scoliosis and improve the quality of life ^[22][23][29,30]. However, due to the complexity of PSSE physiotherapy and research limitations, it is difficult to draw conclusions about the effectiveness of this therapy, and many researcheuthors have emphasized that high-quality research on the effectiveness of physiotherapy in scoliosis treatment is lacking ^{[24][25][26][27]}[31,32,33,34].

2. Current Work

Adolescent idiopathic scoliosis is a complex orthopedic pathology, which should be treated during the growth period using a targeted treatment plan to achieve optimal therapeutic outcomes. Conservative treatment is still preferred for scoliosis management, which aims to avoid or delay the need for surgical treatment as much as possible [8]. Conservative scoliosis treatment helps to reduce or stabilize the deformity and improve the esthetics of the deformation. Traditional bracing has been beneficial in the management of AIS, but growing evidence suggests that PSSE physiotherapy, based on self-correction, stabilization of the corrected posture, and training of daily living activities, is a more effective intervention. This PSSE physiotherapy is usually performed by following a specific methodology. A resviearchw of the scientific literature revealed some similarities between the PSSE physiotherapy methodologies. In the Lyon and FED methods, PSSE physiotherapy is used as an adjacent therapy; bracing is the main treatment in the Lyon method ^[15][28][15,71], while the FED method involves mechanotherapy using a specific apparatus ^[29][49]. The SEAS methodology, which does not emphasize bracing, has been developed based on the Lyon method, and was modified over time according to scientific discoveries ^[15][30][15,72]. The DoboMed method focuses on exercises to increase chest kyphosis, which is typical of the Lyon method ^[31][73]. This method uses a “derotational” breathing that was first applied to Schroth, the most widely studied among the PSSE physiotherapy techniques. The Schroth technique is primarily based on isometric muscle contraction exercises aiming to rotate, lengthen, and stabilize the spine ^[15][32][15,19]. The BSPTS method was formed following the principles of the Schroth methodology, and includes cognitive, sensory, and kinesthetic training [14]. The Side Shift technique is based on special corrective trunk side shift exercises ^[19][26], and the FITS methodology was developed in accordance with the principles of various PSSE physiotherapy schools ^[31][73]. All the mentioned methodologies more or less focus on applying corrective exercises in three planes, developing spinal stability and balance, breathing exercises, and posture awareness. The effectiveness and scientific validity of PSSE physiotherapy depends on the applied methodology. Over the last decade, scientific publications have focused mainly on Schroth and SEAS, but less on FED and BSPTS, and very little attention has been paid to the DoboMed, Side Shift, and FITS methodologies. Some of the  reviewed publications did not differentiate between the used methodologies, and regardless of the methodology used, the results were presented in the context of PSSE physiotherapy ^[27][33][34,59]. A meta-analysis by Thompson and co-researcheuthors revealed that PSSE physiotherapy caused a statistically significant reduction in the Cobb angle; however, many of the studies reviewed by these researcheauthors had a high risk of bias and followed a low-quality protocol ^[33][59]. The meta-analyses performed by other researcheuthors to investigate the effects of PSSE physiotherapy failed to produce reliable results due to the high heterogeneity of the examined studies ^[25][27][34][32,34,48]. Some studies considered interventions, such as the trunk stabilization exercise program, as PSSE physiotherapy ^[35][68], while some used trunk stabilization exercises in the control group ^[36][38]. Thus, it is appropriate to analyze the effectiveness of PSSE physiotherapy methodologies separately in order to obtain evidence of higher quality. The effectiveness of PSSE physiotherapy methodologies has traditionally been measured based on the following two main indicators: Cobb angle and ATR. Park and co-researcheuthors observed a higher effect for the Schroth methodology when the therapy lasted for more than 1 month ^[34][48], whereas Burger and co-researcheuthors noted higher effectiveness for this technique in short-term studies ^[25][32]. Considering that the scoliosis treatment plan lasts on average 2–3 years, it is important to evaluate the effectiveness of the methodologies in the long run. Long-term studies have revealed the statistically significant effect of the SEAS, BSPTS, and Schroth methodologies in the treatment of AIS. A study by Negrini and co-researcheuthors ^[37][45] demonstrated that the Cobb angle increased by 1.70° ± 7.24° in the experimental group during 25 months of treatment (p < 0.05 between groups). In a study on BSPTS, Zapata and co-researcheuthors noted that the effectiveness of the methodology was evident after 1 year, but after 6 months, the difference in Cobb angle between groups was insignificant ^[38][56]. A study on the effectiveness of Schroth showed not only stabilization of scoliosis but also regression ^[37][39][44,45]. In an 18 month study, Cobb angle decreased in 17%, stabilized in 62%, and increased in 21% of participants in the Schroth group; however, the sample size of the study was small (n = 48) ^[40][41]. Shah and co-researcheuthors ^[41][39] compared Schroth and SEAS methodologies and found a statistically significant advantage of Schroth between groups (p < 0.001), but this study also used a small sample (n = 30), and lasted only 7 weeks. The finding of this istudy is in line with the observations of Burger and co-researcheauthors ^[25][32] that the effect of the Schroth methodology is often stronger in shorter-term studies. In any case, more detailed studies are needed to support the effectiveness of the Schroth, SEAS, and BSPTS methodologies, and the scientific validity of other methodologies in the reviewed publications is questionable. Evidence in peer-reviewed publications is insufficient to assess the effect of PSSE physiotherapy methodologies on ATR and quality of life. A meta-analysis by Thompson et al. revealed that patients who received PSSE physiotherapy showed a mean reduction in ATR of 4.4° ^[33][59]. However, the studies included in their analysis had a high risk of bias. A resviearchw of recent clinical trials showed that the use of the Schroth methodology alone caused a significant reduction in ATR ^[29][36][42][38,43,49]. However, the analyzed data were obtained from a small sample and short-term studies. In other studies, no significant difference in ATR was observed between groups. Studies evaluating the effect of PSSE physiotherapy on quality of life showed that it had a positive impact on the domain of functional activity (two long-term studies on Schroth and SEAS ^[40][43][41,47]) and the domain of mental health (a long-term study on SEAS ^[43][47]). Two other short-term studies showed that Schroth was more effective than the control intervention in improving the overall SRS-22 score or the treatment satisfaction domain alone ^[36][44][37,38]. However, more detailed research is needed to confirm the correctness of these conclusions. The comparison between different PSSE physiotherapy methodologies is limited in the reviewed publications. In one study, Shah and co-researcheauthors ^[41][39] found a statistically significant advantage of Schroth over SEAS, and in another study ^[29][49], Nisser and co-researcheuthors found that FED had an advantage over FITS. One researchview also investigated PSSE physiotherapy techniques with the aim of identifying the superior treatment ^[45][74]. According to the researchers uthors, the SEAS and DoboMed methodologies are inferior to Schroth and Side Shift. This was attributed to the development of the Schroth and Side Shift program for a specific deformity and type of scoliosis; however, such conclusions are not based on specific statistics. The researcheauthors cited three studies to support their argument ^[42][46][47][43,50,70], but none of the studies compare the methodologies with each other or examine them in parallel. In addition, although the SEAS methodology does not have a separate classification of spinal deformities, its protocol involves active self-correction and personalization of physical exercise for each patient [18]. As a result, the validity of the findings presented in the publication is questionable, and the evidence provided for the advantage of Schroth and the FED over other methodologies requires more investigation.